Glaucoma is a debilitating disease that results in loss of vision for an estimated 65 million people worldwide. Glaucoma is the second leading cause of blindness in the U.S. and the leading cause of preventable blindness. Yet, only half of the people with Glaucoma know they have the disease. Glaucoma is principally defined by damage to the optic nerve, the ultimate pathway for visual information after processing by the retina at the posterior aspect of the eye. Of the many risk factors for this optic neuropathy, perhaps the most significant is elevated intraocular pressure (IOP). Because IOP is strongly implicated in the pathogenesis of glaucoma, and because treatment involves lowering patients' IOP, methods of precisely monitoring real-time pressure changes are critical for treatment of this disease. This task is complicated by the very sensitive pressure measurements required to detect abnormal pressures in the eye (e.g., normal eye pressure typically ranges from 10–21 mmHg, averaging about 15 mmHg with a ±mmHg deviation), and the invasive nature of current intraocular pressure sensors.
There is no known sensor on the market for the constant real-time measurement of these small intraocular pressures. The potential of such a sensor is that measurements can be made for years for ongoing monitoring of glaucoma treatment. For example, current tonometry techniques involve indirect measurement of IOP. The tonometers used in common practice are difficult to implement for regularly monitoring pressure fluctuations and treatment progress because they rely on skilled operators using external measurement devices that requires constant out-patient treatment and provides only intermittent monitoring of the IOP. In response to the deficiency of current measurement methods, many micromachined or “MEMS” pressure sensor designs have been proposed. MEMS devices are of interest because in principal the small scale of MEMS devices allows for the implantation of a sensor for constant IOP monitoring. These microfabricated devices can provide accurate and precise pressure readouts, but conventional designs all require electrical circuitry and hermetic sealing, a significant impediment to their implementation. None of the IOP sensors proposed solve the two principal difficulties of these devices; power consumption and biocompatibility.
Accordingly, an improved sensor for providing faithful IOP measurement inside the eye without the twin problems of power consumption and biocompatibility is needed.